The advent of high-speed, cell-based, connection-oriented Asynchronous Transfer Mode ("ATM") networks creates a need for a reliable and flexible multicast mechanism that can support traditional LAN-based applications. Multicast functionality is required for implementation of "webcasting," routing, address-resolution and other inter-networking protocols. One of the early contributions to the ATM forum, "LAN Emulation's Needs For Traffic Management" by Keith McCloghrie, ATM Forum 94-0533, described multipoint connections in support of multicasting as one of the high-level requirements for LAN emulation. Such requirements may be viewed as including at least the same level of performance from an emulated LAN as from a traditional LAN in all respects, including multicast capability.
Known techniques for implementing multicast generally fall into two categories: "slowest-leaf wins" and "best-effort delivery." Slowest-leaf wins implies that the slowest leaf of the multicast connection determines the progress of the entire connection. While this technique prevents cell loss, it may be undesirable from the point of view of public-carrier networks where it is important to avoid allowing an arbitrary end-system from controlling the performance of the network. "Best-effort delivery" implies that cells are dropped for leaves that are unable to maintain a predetermined pace. While this technique prevents an arbitrary leaf from controlling the performance of the network, dropping cells in order to maintain performance may also be undesirable, as for example with loss sensitive transfers such as computer data transmission. While these techniques might be suitable for some multicast applications, neither technique provides a satisfactory multicast mechanism for the broad range of applications encountered in high-speed networks.